Assuming total Karachi population of over 150,000 (1998 Demographic Survey of Pakistan) of all age groups, and taking incidence of 20% (+/- 105 bound of error) of pulmonary hypertension and ARDS at 95% confidence interval, we extricated a sample size to be 91 cases (with 91 controls). Epi-info version 1.1 was used to calculate sample size. Actual sample size 182.